tach issues

[not enuf toys]

96 5.7lx 4 bbl mercruiser 21 pitch 3 blade SS

so WOT was getting to about 5200 (if i would let it). this had happened everytime i took it out this year. engine sounded high, speeds were 57 - 58 (verified on 2 different gps). everything sounded about right

had an issue 2 weeks ago with killing the battery while sitting too long having too much fun...if thats possible

come to find out when i got home that the battery may not have been that dead rather the el cheapo battery quick disconnects were garbage and were not making good contact with the main battery posts. all of the other electrical that were running off the secondary posts were running fine (even though amps were low)

so i cleaned up the main posts and replaced the terminal connectors on the main battery wires

now where the strange tach issue occours...

the rpms are 4200 to 4400 and the speed is still the same (still verified).

so my options are ~ pull out the tach and have it tested or check the rpms of the engine and verify to the tach.

where would you start?

motor sounds to be running the same rpms (i can hear the difference inbetween 1000 rpms, or atleast i think i can)

what do you think happened here?

i haven dug into it at all yet as i just noticed this monday. what does this tach get its pickup from? is it old enough to pick up from the alternator?

 

[not enuf toys]

Re: tach issues

im almost thinking maybe i was never running at 5200 but was having electrical issues the whole time because of the terminals.

the gear ratio is 1.47 ~ with a 21 pitch rapture prop is 5200 possible?

i bought the boat early this spring so i have nothing to compare the differences to (for this particular boat

the boat came with a spare alum 19 pitch prop...

she seems to come out of the hole just fine but maybe...just maybe she will come out even faster and if 4200 now is correct, lets get her back up to 4600 4800 where she belongs...

i need to test the tach or engine....

 

[Robbabob]

Re: tach issues

I'm more of a prop guy and this link to in the prop forum may help http://forums.iboats.com/showthread.php?t=287818

Usually you go down an inch in pitch when changing from aluminum to SS due to the better grip found with SS. However, your speed can't be denied!!! check the tach and report back.

Good luck!

 

[not enuf toys]

Re: tach issues

I'm more of a prop guy and this link to in the prop forum may help http://forums.iboats.com/showthread.php?t=287818

if this helps:

1) Performance issue you are trying to correct.
~ more i am trying to understand where i am running and if the current 4200ish is, i will go to a 19 to get the WOT more on track - more holeshot is always a good thing! if 5200 was correct i dont want to goto a 19 and over rev

2) Current prop manufacturer, model, aluminum or stainless as a minimum.
~ Michigan Wheel Rapture SS

3) Current prop diameter and pitch (required).
~ 14.25r 21

4) Wide open throttle RPM and speed with an average load (very helpful)
~ was 5200 (before battery terminal issue) now 4200 (after full charge and replacing terminals) same load same speeds 57 - 58

5) Engine/drive make, model, year, and HP
~ 5.7lx murcruiser alpha I gen II 1996 250hp

6) Boat make model, year, length and weight
~ rinker captiva 212, 1996, 21, boat on trailer is 4400 and i am assuming the single axle trailer weights around 600 - 650 thus boat around 3800


Is it possible that the tach was acting incorrect (high) because of the bad contacts on the main posts?

at the end of the day i want the WOT correct. what was or what is what ever is correct and acurate. if now is correct i will drop to a 19, if was correct i was just keeping it out of 5200.

at what point will the governer in the engine stop rpms? when do the valves start to float on this engine? it has never gotten to a floating valve point...

hmm....the more i say it, sounds like it may now be correct...

what to test first, tach or engine? which is easier?